I've been doing a lot of online searching about building a HERMS. I've noticed that just about everybody uses 1/2 or 5/8 copper coils in their HLT or HERMS tank to circulate their wort through. My question here is this: instead of circulating wort through the coil, why, why don't you circulate the hot water through a coil (say my 3/8 IC) inside the mash tun? My thought here is that it is easier to clean the outside of the coils off. If the mash temp is too high, shut down the water, and you wouldn't have wort still cooking away inside the coils in the HLT. I do realize that heat distribution in the mash would take longer to hit an equilibrium. Maybe a slow motorized mash paddle could solve this.
The reason I'm thinking about this is that I wouldn't have to build another coil for my brewery saving me a chunk of change since 1/2 and 5/8 copper are a bit pricey.

Some people do use their immersion chiller as a HERMS coil. All the recirculation of the mash is taking place pre-boil, so there's really no worry about sanitizing the interior of the coils. If you're using the same IC to chill the wort, it's going into boiling wort for 15-20 minutes, and then you're going to flush it out for a few minutes running water through it.

As you mentioned, the trouble is the thermal mass, You want to have a large thermal mass acting on a small thermal mass in order to get quick equilibrium, especially when the temperature differential is small.

Also, I don't have wort "cooking away" inside my coil when I brew because I always have the pump running and cycle the heat on and off. The wort never sits and cooks like you are suggesting.

As for stirring the mash to get better temp.... I thkn you would lose one major benefit of recirculating mash systems; wort clarity. When you recirculate, you are essentially vorlaufing for the entire mash. You would not believe how clear your wort is at the end of the mash because you have let the grain bed settle and are just filtering over and over and over through it.

In a lighter colored beer, I can look down through the wort at the top of my MLT and see the grainbed below it. Like a nice clear lake....

It's been pretty well documented that the clarity of the runoff has nothing to do with the clarity of the finished beer. It won't stay clear for long anyway. Throw some hops in there for the boil followed by a slug of yeast after cooling and it will be anything but clear. I've seen lots of brilliantly clear beer made using batch sparge methods where the brewer only vorlaufs briefly before running off the wort. I do agree that continuous circulation will normally yield a very clear wort, but I think the main advantage is for temperature control.

It's been pretty well documented that the clarity of the runoff has nothing to do with the clarity of the finished beer. It won't stay clear for long anyway. Throw some hops in there for the boil followed by a slug of yeast after cooling and it will be anything but clear. I've seen lots of brilliantly clear beer made using batch sparge methods where the brewer only vorlaufs briefly before running off the wort. I do agree that continuous circulation will normally yield a very clear wort, but I think the main advantage is for temperature control.

Yeah, but the thing about "pretty well documented" things is that I sometimes find my personal experience to be very different. I trust my personal experience over documentation.

Yeah, but the thing about "pretty well documented" things is that I sometimes find my personal experience to be very different. I trust my personal experience over documentation.

So you are saying that there is a correlation between clear runoff and the clarity of the finished beer then? I wonder why this conflicts directly with what the experts have to say on the subject. Very strange.

Indeed... in my personal experience, my finished beer has been clearer since I started brewing with a HERMS system, despite what the experts say. That's exactly why I said I trust my personal experience more than anything anybody else has written.

I'm not saying I'm right and they're wrong. I'm just saying that I trust what I see coming out of my taps.

I read in some other online brew page that this one guy had his 3/8 tubing get clogged when he was circulating his mash through it...that sounded sorta strange to me. I would think that with the flow you would have it would clear the debris. Also, the only way I can see 3/8 getting clogged is if you didn't grind the gain or use a mash tun. I would think the particles would be very small considering my FB has 3/32 holes.
I do wonder if there is a benefit in heat transfer between 3/8 and 1/2 though.